A conventional liquid crystal display device includes a plurality of pixel electrodes arranged in a matrix form, an opposing electrode as a common electrode provided so as to face the pixel electrodes, and liquid crystal as display medium provided between the pixel electrode and the opposing-electrode. Such a liquid crystal display device performs a display in the following manner. Namely, an electric potential is selectively written into the pixel electrode, and an optical modulation of the liquid crystal provided between the pixel electrode and the opposing electrode is taken place by the electric potential difference between the pixel electrode and the opposing electrode, and visually recognized as a display pattern.
As a method of driving the pixel electrode, a so-called active matrix driving method is known. In this method, the pixel electrodes provided in the matrix form are each connected to switching elements, and each of the pixel electrodes is driven by the switching element. General switching elements are a TFT (thin film transistor), a MIM (metal-insulator-metal) element, etc.
An active-matrix-type liquid crystal display panel provided in an active-matrix-type liquid crystal display device includes an active matrix substrate and an opposing substrate. In the active matrix substrate, a plurality of scanning lines and a plurality of data lines are provided on a transparent insulating substrate so as to cross each other, and a pixel electrode and a switching element for driving the pixel electrode are formed at each intersection of the scanning line and the data line. In the opposing substrate, an opposing electrode is formed oh a transparent insulating substrate. The active matrix substrate and the opposing substrate are provided with alignment films on their surfaces where the two substrates face each other, and adhered to each other with a liquid crystal layer therebetween.
FIG. 28 shows the structure of each pixel of the active matrix substrate using the TFT as the switching element. A gate electrode of a pixel TFT 1 is connected to a scanning line 2, and the pixel TFT 1 is driven by a scanning signal inputted to the scanning line 2. A source electrode of the pixel TFT 1 is connected to a data line 3, and a display signal is inputted to the data line 3. A drain electrode of the pixel TFT 1 is connected to a pixel electrode 14 and one terminal of an auxiliary capacity, through an auxiliary capacity electrode 28. The other terminal of the auxiliary capacity is connected to an auxiliary capacity wiring 4, and then connected to the opposing electrode on the opposing substrate when a liquid crystal cell is constructed. The pixel TFT 1 and the pixel electrode 14 are provided in the matrix form on the insulating substrate.
FIG. 29 shows one example of the structure of the cross section of the active matrix substrate. A gate electrode 8, a gate insulating film 9, a semiconductor layer 10, a n+-Si layer 11 to be the source and drain electrodes, a metal layer 12 to be the data line 3, an interlayer insulating film 13, and a transparent conductive layer to be the pixel electrode 14 are formed in this order on an insulating substrate 7. The pixel electrode 14 is connected to the drain electrode of the pixel TFT 1 through a contact hole 15 piercing the interlayer insulating film 13, specifically through the auxiliary capacity electrode 28.
In the structure shown in FIG. 29, the interlayer insulating film 13 is formed between the scanning line 2 (the same layer as the gate electrode 8) and the pixel electrode 14 and between the data line 3 and the pixel electrode 14. Therefore, the pixel electrode 14 can be arranged to overlap the data line 3. It is known that such an arrangement can improve the aperture ratio, and reduce an alignment defect of liquid crystal by shielding the electric field resulting from the data line 3.
Next, the process thereafter will be explained with reference to FIG. 30. FIG. 30 is a schematic plan view of a conventional active-matrix-type liquid crystal display device. This view shows the state after a large substrate is divided into cells, each of which corresponds to a display device. In the actual process, the cells are often produced in the state where several cells are arranged in rows and columns.
On a viewing area (within the two-dot chain lines) 17 of a completed active matrix substrate 50, an alignment film of the polyimide family is deposited, and the alignment function is added by a treatment such as rubbing. In an opposing substrate 51, a transparent opposing electrode (not shown) such as ITO (Indium Tin Oxide) is deposited, and then the part corresponding to the viewing area 17 is subjected to the same treatment.
A sealing material (not shown) is applied to the surrounding section of the liquid crystal display panel except for a liquid crystal injection port in such a manner as to surround the panel by the printing method, etc. Further, a conductive material 19 is attached onto an opposing-substrate-use signal input terminal 27 on the active matrix substrate 50. Thereafter, a spacer (not shown) for keeping the cell thickness of the liquid crystal layer uniform is sprayed. Then, the active matrix substrate 50 is adhered to the opposing substrate 51, and the sealing material is fixed by adding heat.
Thereafter, liquid crystal is injected through the liquid crystal injection port, and the liquid crystal injection port is closed with an end-sealing material, thereby completing the panel section of the liquid crystal display device. Then, packaging members such as a source driver 20a for applying a display signal to each data line 3, a gate driver 20b for applying a scanning signal to each scanning line 2, a control circuit (not shown), and a backlight (not shown) are installed, thereby completing the liquid crystal display device. Note that the liquid crystal display device shown in FIG. 30 is not provided with the auxiliary capacity wiring 4.
By the way, the inspection of such a liquid crystal display device usually includes an optical inspection performed in each step of the process, an electrical inspection performed in the step where the active matrix substrate is completed, and a dynamic operating inspection and the electrical inspection, performed at the time when the panel section on which the packaging members such as the driver are not yet installed is completed.
Such inspections are performed so as to prevent materials and operations from being wasted by leaving defective parts in the subsequent process. When a deficiency exists in a device, the device is discarded at this time or repaired by means of laser, etc.
However, with the recent improvement of the production technique, the liquid crystal display panel has achieved ever higher definition, and accordingly a higher technique has been required also in the inspection process.
Specifically, since the terminals for inputting the signals to the data lines 3 and the scanning lines 2 are installed with increasingly smaller pitches, when supplying the signals by bringing the respective terminals into electric contact with pins, a prober of extremely high definition and high cost must be prepared. In addition, there is a case where existence of fine dust on the terminals in the inspection interferes with normal dynamic operations, and the defective inspection is recognized as a deficiency of the panel by mistake. In order to avoid such a case, the inspection must be performed in very clean environments. Consequently, a rise in the total cost has been unavoidable.
In order to realize an easier inspection, the liquid crystal display device shown in FIG. 30 has the following structure. Specifically, this liquid crystal display device includes inspection-use display signal lines 52a, 52b and 52c for connecting the data lines 3 which supply the same signal in the inspection with each other, and inspection-use scanning signal lines 53a and 53b for connecting the scanning lines 2 which supply the same signal in the inspection with each other. The inspection-use display signal lines 52a, 52b, 52c and the inspection-use scanning signal lines 53a, 53b are cut off by dicing the substrate along cutting lines L after the inspection or electrically separated by means of laser cutting, etc. in general (for example, as disclosed in the Japanese Publication of Unexamined Patent Application No. 005481/1995 (Tokukaihei 07-005481; published on Jan. 10, 1995)).
However, this method produces another problem that the number of processes is increased because of the cutting process. Moreover, defective units may be newly generated due to fragments of the wiring pattern and scrap pieces of glass, produced by cutting the substrate. In addition, the area to be cut on the large substrate is wasted in the case of dicing, which is disadvantageous in the number of panels to be obtained.
Further, cutting the substrate may produce a static electricity, thereby possibly causing the switching element to be broken by the static electricity.
For example, a method for avoiding the increase of the number of processes for cutting the substrate was devised. In this method, instead of completely bringing the lines for sending the same signal into electric conduction, switching elements such as TFTs are provided for the lines, and signals for switching on the switching elements are supplied as necessary in the inspection, thereby achieving the same effect as the method where the lines are connected to each other.
For example, the method disclosed in Japanese Publication of Unexamined Patent Application No. 142499/1991 (Tokukaihei 03-142499; published on Jun. 18, 1991) is one of-the methods in which the signals are supplied to the scanning lines and the data lines through the switching elements. In this method, signals are subsequently supplied through the switching elements in the state where the substrate is still a large substrate, the respective pixels are charged, and the signals are subsequently read out through the switching elements, thereby electrically obtaining defect information in the screen.
Since this method enables the detection of a defective active matrix substrate in the process before adhering the active matrix substrate to the opposing substrate, it is advantageous in that the processes are not wasted. However, since it is necessary to accurately readout the extremely small electric signals especially when detecting dot defects, this method has many difficult problems including the design of a sense amplifier, the circuit sequence, and the optimization of the balance between the time constant and the readout time of the pixel TFT. In addition, especially in the detection of display unevenness and a low lit defect, the result obtained by the electrical inspection was much different from that of the inspection where the display is actually performed.
In order to solve the problems, the liquid crystal display panel disclosed in Japanese Publication of Unexamined Patent Application No. 333275/1995 (Tokukaihei 07-333275; published on Dec. 22, 1995) is arranged so that the signals are supplied through the switching elements in the same manner, and the dynamic operating inspection can be performed as conventionally done.
FIG. 31 shows the arrangement of the liquid crystal display panel disclosed in the above publication (Tokukaihei 07-333275). In this structure, five terminals Z1 to Z5 provided near the edge section on the surface of the panel are connected to inspection-use signal lines x1 to x7. Further, TFTs 66 as the switching elements are individually formed for the respective scanning lines 2 between the signal lines x1, x2, x3 and the scanning lines 2, while TFTs 67 are individually formed for the respective data lines 3 between the signal lines x4, x5 and the data lines 3. The signals inputted from the terminals z1 to z5 are sent to pixel sections 60 through the respective TFTs 67 and 66.
With this arrangement, when performing the inspection of the liquid crystal display panel, the panel can be driven by only inputting the inspection signals to the terminals z1 to z5, without supplying the inspection signals to the terminals p of the scanning lines 2 and to the terminals q of the data lines 3 line by line. It is thus possible to save the efforts in the inspection.
However, the structure disclosed in the above publication (Tokukaihei 07-333275) has the following drawbacks in the inspection.
Specifically, as shown in FIG. 31, the inspection-use signal line for supplying the signals to the respective data lines 3 is only x4. Thus, the line defects and the dot defects are detected by performing the monochromatic display of black or white in this inspection.
However, due to the recent improvement of the production technique, the display devices have been required to achieve higher display quality, and strict standards have been provided for the dark defect as well as the luminous dot. The dark defect has several types, and the most frequent one in the normally white method is the defect caused when a leakage occurs between a pixel electrode and the data line 3 which should not supply the signal to the pixel electrode (in general, the data line 3 which supplies the signal to an adjacent pixel). Such a defect is detected when performing the monochromatic display.
In the conventional structure according to the above publication, it is impossible to detect such a dark defect, because different signals cannot be supplied to the adjacent data lines. In recent years when display devices have achieved ever higher definition, with the densification of the pattern and the increase of the pixel number, the defect of this type cannot be neglected.
Further, in the conventional structure disclosed in the above publication, since different signals cannot be supplied to the adjacent data lines, the leakage between the data lines 3 cannot be detected.
In order to detect the leakage defect between the data lines 3, the electrical inspection as well as the visual inspection must be performed. One reason for this is that the line defect is much more serious than the dot defect. Another reason is that there is a danger that the defect which was not detected in the visual inspection due to the variation with time of the leakage part and the temperature characteristics of the leakage current may cause a problem on the market.
In addition, like the liquid crystal display panel disclosed in the above publication (Tokukaihei 07-333275), in the case where the inspection-use signals are supplied to the data lines or the scanning lines through the switching elements, the data lines and the scanning lines must be electrically independent of each other after the liquid crystal display panel is completed. Therefore, when a leakage is caused in the switching element, a deficiency in the display and a malfunction may occur.
Further, when a static electricity enters the wiring for supplying the inspection-use signals to the data lines and the scanning lines through the switching elements, an electrical breakdown may occur between the gate and drain or between the gate and source of the switching elements due to a high voltage, thereby possibly causing the leakage defect mentioned above.
There has conventionally been an active matrix substrate in which a static-electricity breakdown of the substrate is prevented by connecting the data lines or the scanning lines with a resistive element so as to let the static electricity generated in a specific line escape into another line, thereby dispersing the static electricity. However, such an active matrix substrate has such a problem that when supplying the signals to the data lines or the scanning lines through the inspection-use wiring in inspecting the active matrix substrate, a voltage applied to the data lines or the scanning liens is decreased by a voltage drop in the inspection-use wiring.
In addition, the inspection efficiency is low, because the inspection is performed in such a manner that a plurality of liquid crystal display panels are produced in a state of being a large substrate, the large substrate is cut into individual liquid crystal display panels, and the inspection is performed for each liquid crystal display panel.